In U.S. Pat. No. 2,953,418 a low friction sleeve bearing is provided by winding a single yarn back and forth around a mandrel a great many times. The yarn is of a heat shrinkable material and is first dipped in a resin which is dried before winding. The yarn of the innermost layers is principally of Teflon to provide the low friction face of the bearing. Winding a single yarn is a tedious process but the dried resin allows the winding to proceed with some speed. However, the finished bearing has very little resistance to crushing. That is, it has very low axial strength because the yarn has a near zero winding angle with the result that the yarn provides practically no reinforcing in the axial direction. Also, the predried resin may not fully fill the yarn in curing and will leave air gaps.
In U.S. Pat. No. 3,616,000 a low friction fabric sleeve is fitted on a mandrel and parallel roves of glass filaments form a tape which carries the liquid resin to the work. The tape is wound over the fabric in layers to form a composite of glass filaments and interstitial liquid resin. The resin is cured and hardens and the glass filaments provide the optimum balance of axial and circumferential reinforcing.
The winding tension is important in that the roves must press against the fabric placed on the mandrel and further conform the fabric to the mandrel and fill the fabric with resin. However, a problem is presented in attempting to make a bearing having an internal spline or threads. The mandrel then includes reentrant portions which the roves will span and unavoidably leave a "resin gap" having no reinforcement and possibly leave an air gap with no resin whatever. In U.S. Pat. No. 3,713,932 the fabric which is applied to the mandrel is shaped by first winding resin impregnated cords in the grooves to assure that the fabric is well conformed to the profile of the thread. This first step must be done with great care so that the teeth of the threads at least will be well filled with resin. A similar problem is presented in trying to provide a bearing for a linear actuator having, for example, a 30.degree. pitch.
A most important object of the present invention is to provide for winding of the filament reinforcing across the grooves in both directions and without leaving any resin gaps in either direction. Another object is to conform the low friction lining material of the collar or nut with the grooves of the mandrel in the winding step. Another object of the present invention is to eliminate having to conform the fabric as in U.S. Pat. No. 3,713,932. Another object is to provide a linear actuator having a relatively large pitch angle. Another object is to improve the fit and support of the collar on the shaft so that the conversion of linear to rotary motion is effected with very little loss due to friction. Another object is to provide an actuator which can be of a relatively large diameter and statically support a large radial or axial load.